FRCPath Part 2—Revision Notes on Aspergillus spp.

(Oxford Textbook of Medical Mycology, Ch 10)

1. Genus at a glance

2. Aspergillus Key species, temperatures, toxins & clinical points

Species (complex)

Opt. Temp / Range (°C)

Colony / Microscopy

Major toxin

Salient clinical facts

A. fumigatus

37 / 12-65

Green-blue; columnar uniseriate heads

Commonest invasive isolate; ABPA, CPA

A. flavus

37 / 12-48

Green-yellow; radiate uni/bi-seriate

Aflatoxin

Sinusitis, keratitis, aflatoxicosis risk

A. niger

37

Black biseriate heads

Otomycosis, onychomycosis

A. terreus

25-40

Beige; biseriate + accessory conidia

Ochratoxin

Intrinsic AmB-R

A. nidulans

37 / 2-48

Green with red-brown cleistothecia

CGD infections; AmB-R

A. versicolor

22-26 (opt); ≤40

White→yellow/green; penicillium-like

Sterigmatocystin

Onychomycosis; grows best at room-temp

A. clavatus

37

Long club-shaped vesicle

Extrinsic allergic alveolitis (“malt-worker’s lung”)

EORTC definitions

Proven:

Probable

Green-yellow radiate, compare to A. fumigatus

Cinnamon colored, columnar

3. Epidemiology & reservoirs

4. Pathogenesis (4-step mnemonic I-G-A-T)

1 Inhalation & alveolar deposition

2 Germination when innate immunity fails

3 Angio-invasion → thrombosis, infarction

4 Toxins & hypersensitivity drive allergic / chronic disease

5. Clinical spectrum

Category

Typical entities / notes

Non-invasive

Otomycosis (A. niger), onychomycosis (A. versicolor), allergic fungal rhinosinusitis

Allergic

ABPA (≈16 % asthmatics); EAA by A. clavatus; SAFS

Chronic

CPA continuum: simple aspergilloma → chronic cavitary → fibrosing disease

Invasive

Acute pulmonary IA ± CNS, eye, skin; sinusitis; mortality 50–85 %

6. Diagnosis workflow

  1. Direct / culture: septate 45° branching hyphae; Sabouraud agar 48-90 h.
  2. Serology & biomarkers:
    1. Aspergillus precipitins (IgG)—best single test for CPA/ABPA support .
    2. Galactomannan ELISA / LFD (false-pos with β-lactams) .
    3. (1→3) β-D-glucan (pan-fungal) .
    4. PCR on blood/BAL; combine with GM for ↑ sensitivity .
  3. Imaging: HR-CT halo sign → air-crescent; MRI for CNS/sinus.
  4. Histology/BAL/biopsy for EORTC “proven” disease.

7. Antifungal susceptibility & resistance

8. Management cheat-sheet

Condition

First-line

Key alternatives / notes

Invasive aspergillosis

Voriconazole

Liposomal AmB; isavuconazole (non-inferior; shortens QT c)

ABPA

Oral steroids ± itraconazole/posaconazole

CPA

Long-term oral triazole; monitor levels

Onychomycosis / Otomycosis

Topical clotrimazole ± oral azole

Surgical

Resection of solitary aspergilloma; debridement of sinus/CNS masses

Supportive: remove colonised lines, taper immunosuppression, give G-CSF if neutropenic.

9. Prognosis & prevention

10. High-yield exam pearls

  1. Columnar uniseriate head + growth to 65 °C = A. fumigatus.
  2. Accessory conidia → think A. terreus (and AmB-R).
  3. Galactomannan false-positive with piperacillin-tazobactam or Penicillium.
  4. Sterigmatocystin ↔ A. versicolor; ochratoxin ↔ A. terreus; aflatoxin ↔ A. flavus.
  5. Report isolates as “A. fumigatus complex” unless molecular ID performed (≥ 40 cryptic species) .
  6. Isavuconazole shortens QTc (contrast other azoles).
  7. Memorise EORTC/MSG 2008 possible/probable/proven definitions—frequent SAQ.
  8. Environmental reservoirs (damp concrete, carpets, HVAC) explain hospital outbreak questions.
  9. Room-temperature growth (~25 °C) onychomycosis isolate? Think A. versicolor.